Process for the manufacture of hydrocyanic acid



Patented Oct. 26, 1937 PROCESS FOR THE MANUFACTURE .OF HYDRQCYANIC ACID Emil Hene, London, England No Drawing. Application June 19, 1934, Serial No. 731,289. In Germany June 10, 1933 Claims.

The invention relates to the manufacture of hydrocyanic acid. It is known to produce alkalicyanide compounds by heating potassium sulphocyanide with zinc powder. But this process is 5 slow and the output of the acid is very insufficient. The process must be also conducted at a high temperature of over 900 C.

These disadvantages are obviated by the invention, which comprises subjecting a mixture of one of the class of reversibly convertible compounds consisting of thiourea or its derivatives, for instance, ammonium sulphocyanide with finely divided copper to a two staged heating treatment. In the first stage of the process the mixture is rapidly heated to a temperature of about 200-400 C. preferably to about 360 C. and in the second stage of the process the temperature is increased to about 600 C. Instead of copper also copper alloys may be used.

If thiourea is employed the conversion takes place essentially according to the following equation:

If ammonium sulphocyanide is used, the following reaction takes place:

The quicker the temperature range of between 200-300" C. is reached in the first stage of the process, the better is the yield of HCN. The temperature should, therefore, be raised at a rate of at least 50 C. per minute.

The output of HCN may be further improved by the addition of paraffin or substances containing the same, for instance, bitumen, petroleum, etc. to the initial mixture.

If the metals or alloys melt at the reaction temperature, they may be employed in an atomized condition; or the thiourea or ammonium sulphocyanide may be sprayed upon the surface of the molten charge, whereby excellent conditions of reaction are obtained. As in the process essentially CuzS is formed the copper can be easily recovered in the finely divided state by roasting and reducing the residues of the process.

The copper or the copper alloys may be also precipitated in the known manner on inert carriers, for instance, silica gel.

50 The invention can be put into practise in the following manner:

Thiourea or ammonium sulphocyanide is sprayed on finely divided copper; paraffin, petroleum or bitumen are added and the mixture is charged into a rotary furnace. It is then heated at a temperature of about 350 0., whereupon the temperature is raised to about 500 0.

Example 1.5 parts thiourea are mixed with 2.6 parts finely divided copper bronze; 0.5 part infusorial silica are added; the mixture is preferably under introduction of air heated to about 360 C. for about 45 minutes; the temperature is then slowly raised to about 600 C.

The gases escaping from the reaction contain HCN, NH3 and a small quantity of CS2.

To obtain pure I-ICN the gases are passed through a rotary drum which is charged with a mixture of ammonium sulfate and concentrated sulphuric acid and heated to a temperature of 80-100" C. If this process is conducted according to the counter-current system, at one end of the drum the dry ammonium sulfate and at the other end the ammonium-free hydrocyanic acid are discharged.

The CS2 may be removed in the usual manner through lead carbonate, ammonium sulphite or bisulphite.

The initial mixture may be employed in the shape of briquettes or tablets.

The residues of this process consist essentially of CuzS, which by roasting and reduction is converted into finely divided copper. This conversion may take place in the same apparatus, where the production of the HON was carried out.

The invention allows a very economical production of I-ICN from nitrogenous lime as simple methods are known to convert the same into thiourea.

A further particular advantage is gained thereby insofar as the thiourea, which is produced in this manner, contains nitrogenous substances, which are made use of in the production of the HCN. As the HON resulting from this process can be easily converted into ferrocyanic cornpounds or sodiumcyanide, the invention affords a simple way, to obtain highly valuable nitrogen containing compounds from cheap nitrogenous, lime. The dry ammonium sulfate obtained at the same time forms a cheap basis for the manufacture of other ammonium salts.

Copper and aluminum have been found to be suitable materials for the apparatus to be used for carrying out this process.

What I claim is:

1. The process for manufacturing hydrocyanic acid, which consists in rapidly heating in a first phase of the process a mixture of one of the class of reversibly convertible compounds consisting of thiourea and ammonium sulphocyanide with finely divided copper up to a temperature ranging between 200 C. and 400 C. and slowly increasing in the second phase of the process the temperature to about 600 C.

2. The process for manufacturing hydrocyanic acid, according to claim 1, which consists in heating the mixture in the first phase of the process to a temperature of about 350 C.

3. The process for manufacturing hydrocyanic acid, which consists in rapidly heating in a first phase of the process a mixture of one of the class of reversibly convertible compounds consisting of thiourea and ammonium sulphocyanide with finely distributed copper deposited on an inert carrier up to a temperature between 200 C. and 400 C. and slowly increasing in the second phase of the process the temperature up to about 600 C.

4. The process for manufacturing hydrocyanic acid, which consists in rapidly heating in the first phase of the process a mixture of thiourea with finely divided copper up to a temperature of about 350 C., slowly increasing in a second phase the temperature up to about 600 0., and regenerating the copper, which is contained in the residue of the reaction by roasting and reduction.

5. The process for manufacturing hydrocyanic acid, which consists in rapidly heating in the first phase of the process a mixture of ammonium sulphocyanide with finely divided copper up to a temperature of about 350 C., slowly increas- 

